Field of the Invention
This invention relates to the field of decontamination and more specifically to the field of decontaminating water in vessels using methylmorpholine-N-oxide.
Background of the Invention
Refineries and petrochemical plants are commonly contaminated with dangerous and reactive sulfur compounds such as H2S and pyrophoric iron sulfides. These compounds are typically mitigated or removed as part of decontamination procedures, for instance, prior to vessel (e.g., large storage tanks) entry by individuals. A conventional approach to decontamination is to use hydrogen sulfide scavengers (e.g., liquid scavengers) such as triazine, acrolein, or formaldehyde. Such scavengers may rely on non-oxidative complexation and may be an economical approach for H2S mitigation. Liquid scavengers may tie up H2S as water-soluble compounds that may be discharged to wastewater treatment facilities. However, such scavengers have drawbacks. For instance, some of the reaction products may not be water-soluble, and some of the treatment chemicals may have associated toxicity or environmental restrictions in certain locations. In addition, only acrolein typically neutralizes pyrophoric iron sulfides. Triazine treatments may raise the pH of effluent streams and as a result, may promote the formation of scales on metal surfaces. Formaldehyde reactions with H2S typically produce water insoluble products. Acrolein benefits may be tempered by its toxicity.
Other methods have been developed and demonstrated to be effective at oxidizing and eliminating H2S and pyrophoric iron sulfide. Such methods include using permanganate (e.g., potassium permanganate), persulfate, sodium nitrite, ozone, hypochlorite, adducts of peroxide such as perborates and percarbonates, and long-chain amine oxides. The oxidizing chemicals may irreversibly convert H2S to harmless water soluble forms of sulfur, which may be compatible with effluent discharge. Each of these scavengers and oxidizing compounds (i.e., oxidizing chemicals) have certain drawbacks. For instance, considering the strong oxidizers, persulfates may be corrosive. Hypochlorite may form dangerous chlorine compounds. Ozone and permanganate may require field mixing, and permanganate decontaminations may be further complicated by large amounts of reaction solids that are typically processed at additional cost. Sodium nitrite may produce ammonia as a by-product, which may stall the sulfide oxidation before it is complete. For perborates and percarbonates, field mixing or solutions prepared with stabilizing agents are typically used. Percarbonates, as with permanganate, may also be exothermic in their reaction, which may be particularly dangerous if hydrocarbon vapors are present. It is to be understood that long-chain amine oxides often include large volumes and may produce excessive foam. Permanganate produces solid manganese dioxide as a reaction product that is typically processed at added cost. Treatments using strong oxidizers are typically accomplished in small sequential batches outside the storage vessel in order to control the associated exotherm. As a result, these treatments may involve considerable time and therefore cost. However, these compounds may also react violently with hydrocarbon components that may be present in sour sludge. Strong oxidizers (i.e., permanganate, percarbonate, persulfate) may be quite non-selective in their reaction and may react with many of the hydrocarbon components that may exist in the sludge that typically is contained in storage vessels. As a result, these type treatments are typically accomplished in small sequential batches outside the vessel in time-consuming fashion.
Mild oxidizers such as amine oxides and nitrites may also be effective at irreversibly oxidizing hydrogen sulfide to harmless forms of sulfur while having limited or no effect on hydrocarbons, which is unlike the strong oxidizers. Such mild oxidizers may normally be added directly to the storage vessel since associated reactions are non-exothermic. Such mild oxidizers also have drawbacks. For instance, typical long-chain amine oxides may pose foaming issues due to their surfactancy. These amine oxides may also have limited efficiency for large amounts of H2S, since they are typically diluted in water to prevent gel formation. Nitrites may also have drawbacks, as their reaction with hydrogen sulfide produces ammonia. As a result, the nitrite oxidation reaction may be accompanied by a rise in pH, which at some point may cease the oxidation before it is complete.
Consequently, there is a need for improved methods and products for decontaminating vessels such as sour water tanks.